I dont have a sailboat big enough to need thru-hulls yet, but on this video, they are replacing old brass ones with what looks like polypropylene or other plastic material. Is this the way it is supposed to be done on sailboats?

It is one way of doing it. He is maybe interested in weight saving for his multihull. Bronze is heavy. I would be more concerned about the way he is applying the backing plates to the hull, using 3M 5200, devils glue instead of polyester or epoxy for a proper seating.

It is one way of doing it. He is maybe interested in weight saving for his multihull. Bronze is heavy. I would be more concerned about the way he is applying the backing plates to the hull, using 3M 5200, devils glue instead of polyester or epoxy for a proper seating.

yeah I thought that was different as well. Personally, I would not use plastic fittings to save 50 lbs, especially on a boat that size.